10 Facts about Horseshoe Crabs

JanaShea / iStock / thinkstock.com

JanaShea / iStock / thinkstock.com

With their helmet-like bodies and the fact that they look nothing like the crabs most of us are used to seeing, horseshoe crabs are a pretty fascinating bunch and are definitely worth knowing more about. From their prehistoric roots to their remarkably hued blood, read on to discover 10 fascinating facts about one of the beach’s strangest looking citizen.

Don’t Call Them Crabs
Despite their name, horseshoe crabs aren’t actually crustaceans at all. Rather, they’re invertebrates with hard shells that share a closer relation to spiders than they do to crabs.

Foot in Mouth, Literally
Horseshoe crabs belong to the Merostomata class which means “legs attached to mouth”. That ought to make mealtime rather interesting.

Living Fossils
How many creatures can successfully trace their roots back 450 million years? Not many, that’s for sure. Horseshoe crabs, on the other hand, go back so far that they’re considered living fossils. They’re older than humans and dinosaurs and have barely changed appearance-wise which, when you think about it, is pretty amazing.

The Better to See You With
Horseshoe crabs don’t miss much, thanks to their 10 eyes. They’re also able to see UV light. Their tails have light sensors that keep the crab’s brain synched with day and night and they even have special eyes designed for finding mates. Not bad for an invertebrate.

Step Down, Schwarzenegger
Horseshoe crabs possess over 750 individual muscles and have 113 distinct muscle groups. Considering the fact that they typically measure between 7 and 12 inches, that’s pretty impressive. Also interesting? Females outweigh males. The former usually tip the scales at 5 pounds whereas the latter only weigh in at 2 pounds.

Blue Bloods
The horseshoe crab’s heart is a long tube that stretches along nearly the entire length of its body. Think that’s strange? Turns out that the blood this tubular heart pumps is blue. Not a murky, almost indiscernible shade but an unmistakable shade of baby blue. What’s more is that this unique blood is actually used by pharmaceutical companies to ensure that their intravenous drugs are free of potentially harmful bacteria. So next time you get a vaccine, thank a horseshoe crab.

Adults Only
Regardless of how tiny a horseshoe crab might seem, the only ones you’ll ever spot are well into adulthood. Baby horseshoe crabs spend the first year or two of their lives burrowed in the sand on intertidal flats, emerging briefly in the morning to feed. Only when it’s good and ready (and has molted several times) will it venture out into the deeper waters or out onto the sand.
Better Get a Bigger House
Talk about a multiple birth! Every year, the female horseshoe crab develops around 80,000 eggs which she will then lay in clutches of 5 per tide. Considering the fact that there are 4,000 eggs per cluster and the female lays approximately 20 clusters per year, at least you know that baby horseshoe crabs will never get lonely.

No Steering Wheel Required
The horseshoe crab’s long tail may look menacing but its intended purpose is pretty darn benign. The long, whiplike extension that protrude’s from the horseshoe’s body is actually meant to steer them while swimming and allows them to change directions in the water.

You Don’t Make Friends With Salad
Horseshoe crabs are diehard carnivores who stick to an exclusively meat-based diet heavy on crustaceans, molluscs, and sea worms.

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